From: David Rientjes <rientjes@google.com>
To: Axel Rasmussen <axelrasmussen@google.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
Ingo Molnar <mingo@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
Michel Lespinasse <walken@google.com>,
Vlastimil Babka <vbabka@suse.cz>,
Daniel Jordan <daniel.m.jordan@oracle.com>,
Laurent Dufour <ldufour@linux.ibm.com>,
Jann Horn <jannh@google.com>,
Chinwen Chang <chinwen.chang@mediatek.com>,
Yafang Shao <laoar.shao@gmail.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH v3 2/2] mmap_lock: add tracepoints around lock acquisition
Date: Tue, 13 Oct 2020 12:42:15 -0700 (PDT) [thread overview]
Message-ID: <alpine.DEB.2.23.453.2010131242010.2883230@chino.kir.corp.google.com> (raw)
In-Reply-To: <20201009220524.485102-3-axelrasmussen@google.com>
On Fri, 9 Oct 2020, Axel Rasmussen wrote:
> The goal of these tracepoints is to be able to debug lock contention
> issues. This lock is acquired on most (all?) mmap / munmap / page fault
> operations, so a multi-threaded process which does a lot of these can
> experience significant contention.
>
> We trace just before we start acquisition, when the acquisition returns
> (whether it succeeded or not), and when the lock is released (or
> downgraded). The events are broken out by lock type (read / write).
>
> The events are also broken out by memcg path. For container-based
> workloads, users often think of several processes in a memcg as a single
> logical "task", so collecting statistics at this level is useful.
>
> The end goal is to get latency information. This isn't directly included
> in the trace events. Instead, users are expected to compute the time
> between "start locking" and "acquire returned", using e.g. synthetic
> events or BPF. The benefit we get from this is simpler code.
>
> Because we use tracepoint_enabled() to decide whether or not to trace,
> this patch has effectively no overhead unless tracepoints are enabled at
> runtime. If tracepoints are enabled, there is a performance impact, but
> how much depends on exactly what e.g. the BPF program does.
>
> Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
Acked-by: David Rientjes <rientjes@google.com>
next prev parent reply other threads:[~2020-10-13 19:42 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-09 22:05 [PATCH v3 0/2] Add tracepoints around mmap_lock acquisition Axel Rasmussen
2020-10-09 22:05 ` [PATCH v3 1/2] tracing: support "bool" type in synthetic trace events Axel Rasmussen
2020-10-12 14:15 ` Steven Rostedt
2020-10-12 14:26 ` Tom Zanussi
2020-10-12 14:46 ` Steven Rostedt
2020-10-12 16:23 ` Axel Rasmussen
2020-10-13 19:41 ` David Rientjes
2020-10-09 22:05 ` [PATCH v3 2/2] mmap_lock: add tracepoints around lock acquisition Axel Rasmussen
2020-10-09 22:35 ` Michel Lespinasse
2020-10-10 5:31 ` Yafang Shao
2020-10-13 19:42 ` David Rientjes [this message]
2020-10-20 14:50 ` Vlastimil Babka
2020-10-20 18:17 ` Axel Rasmussen
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